The present invention relates to assays using labeled probe strands with DNA complementary to strands of DNA in a sample to detect the presence of the DNA in the sample by analyzing for the labeled probe strands.
DNA probe assays typically involve analyzing for one or more copies of a first strand of oligonucleotides in a sample by introducing plural second strands of oligonucleotides which are complementary to the first strand(s), so as to hybridize to the first strands if first strands are in the sample. Second strands are labeled (e.g. with phosphorus-32, chemiluminescent compounds such as acridines and luminols, fluorescent compounds such as fluorescein and rhodamine, biotin, and enzymes such as alkaline phosphatase and acid phosphatase, and liposomes containing such labels) so they can be detected in the sample.
One problem in the past with DNA probe assays is in separating the hybridized probe strands from the unhybridized probe strands. A separation system based upon size differences between probe, target, and probe-target duplex works, but the methods used are tedious and difficult to automate. As an example, a Southern blot assay Southern, Journal Molecular Biology, 98:503-517 (1975)! is difficult to automate. Another assay which utilizes size separation is the Abbott Laboratories "Genostics" assay for hepatitis B virus. In the "Genostics" assay, native HB DNA is hybridized to iodine-125 labelled probe. The DNA-probe hybrid is then passed through a size exclusion column with enough volume of eluent to give only the hybrid in solution in a collection flask. The flask is then assayed for radio-isotope by standard methods. Although this method works well, a technician still must run the test. The method, then, is also not amenable to automation. Few satisfactory solutions to the separation problem in automated systems have been proposed.